Where:
I
rms: RMS current corresponding to the largest phase current
IFL: Thermal trip or full load current rating (settable)
k : Settable (1 to 1.5 step 0.01)
A: Initial thermal state (eg. If the initial thermal state is 50% then A =0.5)
The calculation of the thermal state is given by the following formula:
Θi+1 = (Irms /k*IFL) ² · [1 – exp (-t/Te)] + Θi · exp (-t/Te)
The initial state of the machine is included in the time to trip calculation algorithm. This is so that the
operating time for a thermal trip is decreased if there is a hot motor start.
Comprehensive measurements and diagnostics can be accessed through the HMI. For example, the
estimated time to the next thermal trip is calculated (see MEASUREMENT 2 sub menu).
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